Abstract

A rapid signal-fading event produced by diffractive scintillations was observed around 0123 UT on 8 November 2004 by three closely sited (less than 250 m apart) GPS scintillation receivers in northern Norway. The entire duration of the event was about 10 s and was recorded by all three receivers. Intense, short duration events such as these are not clearly observable in the 1-min scintillation index (S4) because they do not necessarily last for the entire minute. In spite of their short duration they can cause a receiver to lose lock because of their intensity. The geomagnetic conditions were disturbed at this time with the interplanetary magnetic field southward for a period of several hours. Magnetometers from the IMAGE network in Scandinavia showed evidence of a 2000 nT substorm. The GPS measurements are compared with all-sky camera (ASC) data to show that the signal fades can be attributed to the GPS ray paths crossing electron density structures associated with the aurora. The ASC images reveal moving auroral structures at the same time as the GPS signals show movement of the ionospheric regions causing fading. The results indicate that at high latitudes low-elevation GPS signals can suffer sudden fading due to E-region auroral events. This is the first time that a direct connection has been established between the loss of lock on a GPS receiver and diffractive fading caused by auroral precipitation.